Two-dimensional electrophoresis is the preferred method for separating proteins from complex mixtures such as tissue samples, bacteria or plant material. Typically the proteins are separated in the first dimension using an electrophoresis gel with an immobilised pH gradient (IPG). These gels are commercially available and are usually supplied as dry gel strips bonded to a plastic backing sheet. Before the separation takes place the gel must be rehydrated with an appropriate liquid, in which it is ideal to have the protein sample dissolved. The most common embodiment of this approach is to allow the rehydration to occur passively, in a tray comprising a plurality of troughs, until the liquid in each trough has fully rehydrated the IPG gel strip in that trough. This requires that care is taken in selecting the correct volume of rehydration liquid to match the capacity of the IPG gel strip. If too little rehydration liquid is added the IPG will under-rehydrate and the separation will be compromised. Similarly, if too much rehydration liquid is added and some of that liquid is not taken up by the IPG gel strip then proteins are lost in the liquid which is not taken up into the gel. Typically, high molecular weight proteins are preferentially lost in this process.
To overcome this drawback with passive rehydration some groups have advocated the use of rehydration trays with electrodes embedded in the troughs. The electrodes are used to provide a voltage (˜50 V) during the rehydration process. This electric field causes ‘active’ uptake of the proteins into the IPG gel matrix and results in more proteins entering the gel, especially high molecular weight proteins. However, if the rehydration solution comes in contact with both electrodes during the rehydration process, then the dissolved proteins may undergo electrophoretic transport to the electrodes in the free solution. If this occurs, a significant proportion of the proteins of the sample do not separate in the IPG because the sample proteins are transported to the electrode and then precipitate there. The proteins which are lost in this process represent all molecular weights, not only high molecular weight proteins.
The present invention aims to provide an IPG gel strip rehydration tray that allows active rehydration to be done without the free rehydration solution coming into contact with the electrodes, thus preventing the electrophoretic transport of the proteins to the electrodes.